The invention concerns a method for the liquid/liquid extraction of uranium from phosphoric acid with the aid of alkylamine polyphosphate and/or alkylamine metaphosphate compounds, dissolved in organic solvents insoluble in water, in the presence of Fe.sup.II ions.
Mineral acids, among other things, are used for the dissolution of uraniferous ores, which contain the uranium in the dissolved state after the dissolution process. Many efforts have been made in order to remove the uranium from such acids in order to obtain uranium.
During the production of phosphoric acid according to the acid dissolution process, crude phosphoric acids also containing uranium are obtained when using uraniferous phosphate ores. Various methods of uranium extraction from phosphoric acids have become known, e.g., extraction of uranium with the aid of alkyl pyrophosphoric esters and extraction with di (2-ethyl hexyl) phosphoric acid and trioctyl phosphine oxide, the latter process having obtained special significance.
The uranium extraction from phosphoric acid did not have an exonomic significance for a long time, since the uranium concentration both in the phosphate ores and in the acids obtained was too small to be considered profitable.
Consequently, methods were mainly employed for uranium extraction, which process uranium ores of a higher concentration as raw materials. In such processes, among other things, the uranium is dissolved from the mineral and by treating the ore with dilute sulphuric acid, using an oxidizing agent if required, whereby the uranium is transferred into the sulphuric acid. The uranium is then separated from the diluted acid by other process steps.
One of these isolation methods is, for instance, the solvent extraction of the uranium with the aid of higher molecular weight alkylamines. In U.S. Pat. No. 2,877,250, for instance, a liquid/liquid extraction method is described to obtain uranium from aqueous acid solutions with amines, which are dissolved in water-in-soluble non-polar organic solvents. From this it can be seen that a good uranium extraction with amines is possible from such solutions which have a low to mediumconcentration of sulphate, phosphate, fluoride and acetate and a high concentration of chloride as well as a high concentration of nitrate with a medium pH-value. For instance, from a 0.7 molar phosphoric acid (approximately 4.8% P.sub.2 O.sub.5), uranium is extracted to a certain extent according to the known method, while it is not possible any longer to extract uranium from a 1.3 molar phosphoric acid (approximately 8.6% P.sub.2 O.sub.5). Similarly, according to the known method, the concentration of sulphuric acid must be less than 1 molar (approximately 9.4% H.sub.2 SO.sub.4) in order to obtain quantities of uranium worth considering.
In addition to this, U.S. Pat. No. 3,409,415 describes a process of obtaining tri-valent lanthanides and actinides from solutions not containing a sulphate by means of organic acids, selected from the group of monocarboxyl, polycarboxyl and amine polycarboxyl acids, with the aid of water-immiscible organic solutions of high-molecular amines. The pH-value of the solutions from which the metal ions are extracted ranges from approximately 2.5 to 10.3.
From Chemical Abstracts, Vol. 85, 1976, 131296d it is known to extract uranium with primary amines in the presence of tetrasodium pyrophosphate. Such an extraction does not take place from a highly acidic solution, but from solutions with a pH-value of 5-7.
The processes of uranium extraction from phosphoric acid with the aid of alkyl pyrophosphoric esters and with di (2-ethyl hexyl) phosphoric acid and trioctyl phosphine oxide work in an acid concentration range of approximately 5.3 molar (i.e., approximately 30% P.sub.2 O.sub.5).
However, these known methods have the disadvantage of a high chemical consumption due to the instability of the reagent if alkyl pyrophosphoric esters are used. When using di (2-ethyl hexyl) phosphoric acid and trioctyl phosphine oxide, the process, on the one hand, is subjected to high financial expenditures for the acquisition of the reagent, while, on the other hand, extensive process steps for the circulation of the light reagent phase are necessary in order to ensure the continuous operation of the total flow of the uranium extraction.
Consequently, there was a demand for a process suitable to extract uranium from acidic solutions with low to high acid concentration.